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Single-Winner Voting Method Comparison Chart

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Single-Winner Voting Method Comparison Chart Single-winner Voting Method Comparison Chart This chart compares the most widely discussed voting methods for electing a single winner (and thus does not deal with multi-seat or proportional representation methods). There are countless possible evaluation criteria. The Criteria at the top of the list are those we believe are most important to U.S. voters. Plurality Two- Instant Approval4 Range5 Condorcet Borda (FPTP)1 Round Runoff methods6 Count7 Runoff2 (IRV)3 resistance to low9 medium high11 medium12 medium high14 low15 spoilers8 10 13 later-no-harm yes17 yes18 yes19 no20 no21 no22 no23 criterion16 resistance to low25 high26 high27 low28 low29 high30 low31 strategic voting24 majority-favorite yes33 yes34 yes35 no36 no37 yes38 no39 criterion32 mutual-majority no41 no42 yes43 no44 no45 yes/no 46 no47 criterion40 prospects for high49 high50 high51 medium52 low53 low54 low55 U.S. adoption48 Condorcet-loser no57 yes58 yes59 no60 no61 yes/no 62 yes63 criterion56 Condorcet- no65 no66 no67 no68 no69 yes70 no71 winner criterion64 independence of no73 no74 yes75 yes/no 76 yes/no 77 yes/no 78 no79 clones criterion72 81 82 83 84 85 86 87 monotonicity yes no no yes yes yes/no yes criterion80 prepared by FairVote: The Center for voting and Democracy (April 2009). References Austen-Smith, David, and Jeffrey Banks (1991). “Monotonicity in Electoral Systems”. American Political Science Review, Vol. 85, No. 2 (June): 531-537. Brewer, Albert P. (1993). “First- and Secon-Choice Votes in Alabama”. The Alabama Review, A Quarterly Review of Alabama History, Vol. ?? (April): ?? - ?? Burgin, Maggie (1931). The Direct Primary System in Alabama. Masters thesis, University of Alabama. Green-Armytage, James (n.d.). “A Survey of Basic Voting Methods”. Web page at http://fc.antioch.edu/~james_green-armytage/vm/survey.htm (last visited November 20, 2008). Green-Armytage, James (2008). “Strategic Voting and Strategic Nomination: Comparing seven election methods”. Unpublished manuscript, University of California at Santa Barbara. http://econ.ucsb.edu/graduate/PhDResearch/electionstrategy10b.pdf (last visited November 20, 2008). Nagel, Jack (2007). “The Burr Dilemma in Approval Voting”. Journal of Politics, Vol. 69, No. 1 (February): 43-58. Robert, Henry M., William J. Evans, Daniel H. Honemann, Thomas J. Balch (2000). Robert's Rules of th Order Newly Revised, 10 Edition. Cambridge, MA, Da Capo Press. Tideman, Nicolaus (2006). Collective Decisions and Voting: The Potential for Public Choice 1 Plurality Voting is the most prevalent method of voting in the U.S. In a single seat election, the voter picks one candidate, and the candidate selected by the largest number of voters is elected, regardless of whether that candidate is favored by a majority or not. Because of its supposed similarity to a horse race this method is sometimes referred to as "First Past the Post" or FPTP. 2 Two-round Runoffs are intended to prevent split majorities resulting in the election of a candidate that the majority opposes. The winner of the second round is considered a majority winner, although, due to drop-off in turnout, this "winner" could receive fewer votes in the runoff than the loser received in the first round. Thus the "majority" is manufactured by preventing voters from voting for eliminating candidates and discounting all voters who do not turn out for the second round. 3 Instant Runoff Voting has several variants and other names, including "Ranked-Choice Voting (RCV), Preferential Voting, and the "Alternative Vote." Voters are allowed to rank candidates in order of choice using a single transferable vote. If no candidate is the first choice of a majority of voters, candidates are sequentially dropped from the bottom, with ballots that were credited towards these candidates then being credited to those voters' next choice who has not been eliminated. This simulation of a series of runoffs ends when one candidate receives a majority or only one candidate remains. This method of voting was invented in Massachusetts around 1870, based on the "single transferable vote" innovation developed some decades previously. It is described in Robert's Rules of Order (Robert, et al., 2000: 411-414), and is used for government elections in places such as the U.S., Ireland and Australia. 4 Approval Voting allows voters to vote for as many candidates as they wish in a single-seat election, with the candidate receiving the most votes being elected. Thus some voters may cast one vote, while others effectively may cast several. Since this method is not used in government elections it has not been constitutionally tested as to whether it complies with the one-person, one-vote mandate. 5 Range Voting asks each voter to assign a score (such a 0 - 10) to each candidate, with the candidate with the highest average score being elected. It is used in sporting events with impartial judges and Internet scoring of various products or services. Because this method is highly susceptible to strategy, it is most appropriate when voting is conducted by disinterested judges, rather than voters with a stake in the outcome. 6 Named after the Marquis de Condorcet who invented it around the time of the French Revolution. Voters are asked to rank all candidates. There rankings can be used to do a pair-wise comparison of how each candidate would theoretically do in a head-to-head match up with each other candidate one at a time. If there is one candidate who would defeat each of the others in a one-on-one contest, this candidate is termed the "Condorcet winner." In some scenarios there is no such winner, as a cycle where A would beat B, B would beat C and C would beat A exists (think of rock, paper, scissors). In this case a variety of different procedures (often named for the inventor) have been proposed for settling which candidate should win. 7 Borda Count, named after its inventor Jean-Charles de Borda around the time of the French revolution, asks voters to rank all candidates in order of preference. Based on this order, the candidates are assigned a score, with the first choice receiving the most points, the second choice receiving a smaller, number, etc. with the last candidate receiving no points. In one sense, it is like Range voting, except that the points are inflexibly tied to the ranking order, rather than set by the voters individually. Because it is highly susceptible to strategy, like Range Voting, it is most suitable for elections by impartial judges, rather than voters with a stake in the outcome. 8 Resistance to Spoilers: A "spoiler" is a minor candidate with little chance of winning, that by being in the race, results in a candidate that the majority of voters oppose being elected over a candidate that a majority of voters would prefer. 9 Elections with more than just two candidates are prone to spoiler situations under Plurality rules. In fact, the spoiler concern is raised in most campaigns with more than just two candidates in the U.S. The primary means by which plurality elections resist spoiler scenarios is by suppressing candidacies and restricting voter choice, or convincing voters to abandon their true favorite choice in favor of a "lesser evil." 10 Two-round runoffs were originally implemented to avoid the spoiler scenario, and elect a majority winner, rather than a mere plurality candidate. Two-round runoffs can achieve this goal when the number of candidates is fairly limited. however, because two-round runoffs fail the clone resistance criterion, it is possible for a spoiler scenario to occur in the first round if there are more than three candidates (because it is actually a plurality election with two "winners" who advance), knocking out an otherwise winning candidate from the final runoff. For example: in an election with 100 voters and three candidates, A, B, and C. 32 voters prefer the candidates in the order A>C>B 30 voters prefer the candidates in the order B>C>A 38 voters prefer the candidates in the order C>B>A Candidates A and C advance to the second round with 32 and 38 votes respectively. In the runoff round C wins 68 to 32. However if a fourth minor candidate (D) enters the race who appeals to the supporters of C such that the preferences are as follows: 32 voters prefer the candidates in the order A>C>B>D 30 voters prefer the candidates in the order B>C>D>A 29 voters prefer the candidates in the order C>D>B>A 9 voters prefer the candidates in the order D>C>B>A Instead of advancing to the runoff round, candidate C is eliminated due to the entry of the "spoiler" candidate D, and candidates A and B advance to the runoff, which B wins 68 to 32. 11 IRV is fully resistant to classic spoiler scenarios in which a minor candidate splits off votes from an otherwise winning candidate. However, IRV can still suffer a dynamic similar to the spoiler dynamic when there are three or more candidates with strong support. In such cases it may sometimes be possible that a voter's support for a favorite candidate rather than a "lesser-of- two-evils" candidate may result in the favorite making it to the final runoff instead of the compromise candidate, and yet the favorite candidate may be unable to win in that runoff against a less-preferred choice, whereas the compromise candidate could have won. There are no known examples of this scenario playing out in real world IRV elections, but it is at least conceivable. 12 Approval voting is probably less prone to spoilers than plurality elections, but is not immune.
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